Persistent hunger and dysphoria are among the reasons dieters have shown poor adherence to diet regimens using conventional, moderate restriction of caloric intake. Paradoxically, the total fast or protein supplemented fast have been associated with better adherence, suppression of appetite, and elevation of mood. This anecdotal observation has been attributed to ketosis in carbohydrate free diets. The protein supplemented fast, however, produces several physically hazardous side effects. This investigation is evaluating objectively whether the protein supplemented fast is associated with positive psychological outcomes and whether dieters tolerate this diet better than one with a carbohydrate supplement. Such information could help in evaluating the value of using the protein supplemented fast in the treatment of obesity. Preliminary results on inpatient volunteers showed that the carbohydrate-free diet did not produce an advantage compared with an isocaloric, carbohydrate-free diet in terms of appetite or mood. The investigation is being repeated with outpatients in their natural environments.